In the electronics industry for manufacturing semiconductors, liquid crystals, etc., various CVD processes are used for producing various films such as silicon nitride films, silicon oxide films, silicon oxynitride films, TEOS oxide films, high dielectric constant films, low dielectric constant films, and metal films.
Among these, for example, silicon-based thin films are formed by a CVD method mainly using an explosive and toxic silane-based gas. In this CVD method, after being used in a CVD process, the used process gas as an exhaust gas containing the above-mentioned silane-based gas is rendered harmless in an abatement apparatus as described in Patent Literature 1 below. It is conventional practice to dilute the silane-based gas in the exhaust gas with a large amount of diluent nitrogen gas introduced upstream of the abatement apparatus so as to reduce the concentration of the silane-based gas to a level lower than the lower explosive limit.
Here, in a typical CVD process for forming silicon oxynitride films, SiH4/NH3/N2O=1 slm/10 slm/10 slm (slm: standard liter per minute, i.e., a unit of flow rate of a gas at 0° C. and 1 atm expressed in terms of liters per minute) is used. Since the explosion range of SiH4 is 1.3% to 100%, the gas mixture emitted in this CVD process must be diluted with about 76 parts of diluent nitrogen gas immediately after the emission. After the dilution, a conventional pyrolysis (thermal decomposition) apparatus, for example, a combustion type pyrolysis apparatus or an atmospheric plasma type pyrolysis apparatus can be used to perform abatement treatment safely and reliably.